This invention relates to the preparation of new polymers with controlled amount of sulfonic acid or sulfonate groups.
By introducing ionic groups such as sulfonic acid groups in the polymer chains of water insoluble typis, modified polymers can be obtained which are soluble or dispersible in water. Polymers containing sulfonic acid or sulfonate groups have been found useful as thickeners, impregnating materials, binders, surface coating materials and adhesives. Being polyelectrolytes, they have even potential application as antistatic agents. Further they have also been shown to be applicable as ion-exchange resins and polymeric catalysts due to the presence of active strong sulfonic acid groups.
Two methods have mainly been used for the preparation of polymers containing sulfonic acid groups. One by direct polymerizing with sulfonate monomers such as ethylene sulfonic acid or sodium ethylene sulfonate (SES) and the other by introducing sulfonic acid groups in the existing polymer chains.
The main problem associated with the direct polymerization method is that only small amounts of water-insoluble monomers e.g., acrylonitrile (AN), methylacrylate (MA), methylmethacrylate (MMA) and vinyl acetate (VA) can be copolymerized with SES in aqneous media. However, copolymers of SES with VA and with styrene are readily prepared in agueous dimethylsulfoxide (DMSO). Furthermore it was difficult to control these polymerization processes since SES concentration influences polymerization rate and molecular weight of the polymer.
For this reason the method of introducing the sulfonic acid groups in an existing polymer became dominating. The commonly used substrate for sulfonation of polymers so far was polystyrene. Sulfonation of the styrene units has been carried out by means of sulfonating agents like sulfurtrioxide, chlorosulfonic acid or a sulfurtri oxide complex, where the phenyl groups of the styrene units are sulfonated.
In the literature a number of methods for the preparation of water soluble or water insoluble polystyrene sulfonates have been described (see e.g. U.S. Pat. No. 2,631,127 and 3,259,592 or W.R. Carrol and H. Eisenberg, J. Polym. Sci., A-2, 4, 599 (1966)). The main disadvantages with these methods are to control the quality of the product duct due to the formation of sulfone cross-links between the polymer chains. These cross-links can for example result in water insoluble products instead of water soluble products. Furthermore sulfonation is carried out under rather extreme conditions e.g. from the point of view of reaction temperature and hazardous solvents. Besides the sulfonating agents which are used for such purposes are very reactive and thus need special care for handling and processing.
The object of the present invention is to obtain polymers with controlled amount of sulfonic acid or sulfonate groups by a method which makes it possible to obtain the desired sulfonic acid content in the end product without the formation of sulfone cross-links and which can be carried out under mild conditions.